After "Gadget," the test device exploded at the Trinity site in the desert of New Mexico, these were the world's first actual nuclear weapons. “Little Boy,” on the right, was dropped on the city of Hiroshima. From the beginning of the Manhattan Project the physicists knew that its simple "gun type" mechanism would need no testing, but this design also made it an extremely unsafe and very inefficient weapon, so dangerous that it was decided not to complete its assembly until the plane carrying it, the Enola Gay, had safely departed the huge U.S. military air field on the island of Tinian. "Fat Man," the more elegant "implosion" design, was an improved version of Gadget packed into a ballistic casing (inert devices used for drop testing were code named "Pumpkins"). It was used against the city of Nagasaki. Neither of these weapons was as powerful as the "triggers" of the thermonuclear devices which I maintained, yet even so these relatively crude devices were powerful enough to kill well over 200,000 people! These weapons were the first two nuclear weapons used in war, hopefully they will remain the last.